The invention relates to an FM radio receiver.
A conventional FM stereo receiver has a DC block-coupling capacitor between an FM detector and a stereo multiplex demodulator. The capacitor is provided to eliminate interference between a fixed DC voltage applied to the output terminal of the FM detector and a DC voltage which is applied to the input terminal of the demodulator independently of the DC voltage at the output terminal of the FM detector. The use of such a coupling capacitor, however, gives rise to some stereo demodulation problems. The capacitor reduces the amplitude of low frequency components contained in a stereo composite signal recovered by the FM detector and changes the phase of the components. This results in degradation of a separation between right and left audio signals of a low frequency range which are demodulated by the stereo multiplex demodulator. The degradation brings about the degradation of the separation in medium and high frequency ranges. The separation in the medium and high frequency ranges also changes depending on the presence or absence of the low frequency components. In other words, the separation in the medium and high frequency ranges is modulated by the low frequency components. As a result, the localization of a sound image will become ambigous and unstable.
Accordingly, an object of the invention is to provide an FM receiver with an improved separation characteristic during a stereophonic program reception.